Introduction:
When the salary of an officer is increased by 25%, it means that the new salary is 125% of the original salary. To restore the original salary, we need to find the percentage by which the new salary should be decreased.

Let's solve the problem step by step:

Step 1: Calculate the new salary:
To find the new salary, we need to add 25% of the original salary to the original salary. Let's assume the original salary is S.

New salary = S + 0.25S
= S(1 + 0.25)
= S(1.25)

So, the new salary is 1.25 times the original salary.

Step 2: Calculate the percentage decrease:
To find the percentage decrease needed to restore the original salary, we need to calculate the difference between the new salary and the original salary. Let's assume the percentage decrease is D%.

Difference = New salary - Original salary
= S(1.25) - S
= 0.25S

Now, we need to find the percentage decrease that equals 0.25S.

Step 3: Calculate the required percentage decrease:
To find the required percentage decrease, we divide the difference by the new salary and multiply by 100.

Required percentage decrease = (Difference / New salary) * 100
= (0.25S / S(1.25)) * 100
= (0.25 / 1.25) * 100
= 0.2 * 100
= 20%

Therefore, the new salary should be decreased by 20% to restore the original salary.

Conclusion:
To restore the original salary after a 25% increase, the new salary needs to be decreased by 20%. This can be calculated by finding the difference between the new salary and the original salary, dividing it by the new salary, and multiplying by 100.